Wikipedia:Reference desk/Archives/Science/2011 October 15

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October 15

Highest-temperature superconductor

What's the highest-temperature superconductor? --75.50.55.27 (talk) 03:15, 15 October 2011 (UTC)

See here. Count Iblis (talk) 03:59, 15 October 2011 (UTC)

What's the highest-temperature superconductor that can currently be used on Earth? --75.50.55.27 (talk) 04:03, 15 October 2011 (UTC)

See the sixth bullet point in High-temperature superconductivity#History and progress. Deor (talk) 05:43, 15 October 2011 (UTC)

USS Ponchatoula AO 148

I was stationed on the Ponchatoula back in 1960 to 1964 and we spent some time at Christmas Island for the nuclear test. Now I have hears the ship is listed with the Center for Disease Control. Is this true? Bob Leach — 98.28.74.227 (talk) 04:22, 15 October 2011 (UTC)

Our USNS Ponchatoula (T-AO-148) article seems to indicate she was laid up to reserves. That was in the Maritime Administration National Defense Reserve Fleet Suisun Bay, in Benecia, California, and has since been pulled out and decommissioned in 1992. With disposal ordered in 1999, our article talk page says she was still afloat in 2008, but there is this story she was scrapped in 2003. It's possible, because much how Starfleet imposed a warp 5 maximum speed, the Ponchatoula was found in violation of the Oil Pollution Act of 1990 without a double hull after the Exxon Valdez oil spill. I can see no indication that her nuclear test assistance marred her service record, but more than 100 tests seems like it may be excessive:

"... Support for experimental operations highlighted 1962 as she provided POL services to Joint Task Force 8 engaged in operation Dominic the Christmas Island nuclear test series, then operated Project Mercury recovery ships during the Sigma splashdown...."[1] (emphasis added)

However, the crew plans to re-assemble next year. So try to contact them. I'm not entirely sure why the crew roster is hosted by a German site, but why not. How close did you get to the Operation Dominic blasts? Dualus (talk) 09:26, 15 October 2011 (UTC)

Power of a sneeze

I looked in the artical on sneezing but couldn't find the answer. Is there a way to measure the power or force or energy of a sneeze? If so, what is the average "energy" of a sneeze? 65.160.229.33 (talk) 05:43, 15 October 2011 (UTC)

See http://uclue.com/?xq=1945.

—Wavelength (talk) 06:07, 15 October 2011 (UTC)

Microwave power draw: volt-amps versus watts

According to the manufacturer's plate, my new microwave draws 1600 watts at 120 volts (for a theoretical 13 amps). According to my Kill-a-Watt meter, it's drawing 16.5 amps at 120 volts with a power factor of around 0.75, setting off the meter's overload alarm. It's plugged into a 15-amp outlet connected to a 20-amp circuit breaker.

Is the meter correct in that the microwave is drawing too much power for the outlet, or is the manufacturer correct in that the microwave can run fine off a 15-amp outlet? If I add a four-amp load elsewhere on the circuit (say, turn on the lights), is the breaker going to trip? --Carnildo (talk) 07:24, 15 October 2011 (UTC)

It's not power that your meter is complaining about, it's current. The wiring in the circuit the microwave is on is a resistive load. When current flows through it, the power dissipated on it is $I^{2}R$. That power is dissipated as heat. When it's too high, it may raise the temperatures of the wiring, switches etc. beyond what they are designed to safely handle. --173.49.13.222 (talk) 12:28, 15 October 2011 (UTC)

That doesn't answer the question. There is a discrepancy between the 13 Amps claimed by the manufacturer of the oven and the actually measured 16.5 amps. Which one is correct? There's no way to tell without further tests. Dauto (talk) 14:07, 15 October 2011 (UTC)

I don't actually see a discrepancy. If the device is drawing 16.5 A at 120 volts with a power factor of 0.75, I presume this means it has an apparent power of 1,980VA but a real power of 1,485W which is under the manufacturers max rating so within expected range. I'm pretty sure all devices are rated by their real power, since that is what devices uses and what you pay for (not counting the overall effect and ignoring the tiny amount due to losses in home wiring etc), not the apparent power, although some may mention it (hopefully in VA) or the power factor since it obviously matters in some ways (e.g. to UPSes). However drawing 16.5A from a 15A rates plug & outlet does sound like a problem. It seems something manufacturers need to take in to account when designing a device so I'm surprised, but perhaps the regulations allow it since there must be a safety margin in the ratings, something to check in to in any case. In addition, there could be regulations governing the power factor of devices where you live, you may want to check if your device meets them. Of course, if you're in an industrial setting or otherwise pay something for a low power factor then it may be of additional concern that your device has such a poor power factor, but not for safety reasons. (Utility companies obviously don't like their customers using lots of devices with poor power factors but that isn't of direct concern to you except in an overall way.) Nil Einne (talk) 15:39, 15 October 2011 (UTC)

When you say it's a 15 amp outlet, you mean that both of the flat blades openings in the receptacle are vertical, rather than one being vertical and the other accepting either a vertical or horizontal blade, right? If the breaker is 20 amps, every bit of wiring from the service panel to the outlet must be 12 American wire gauge or greater diameter. If it is 14 gauge, call an electrician and get it fixed. As for which current is correct, I would test with additional instruments or call an electrician. If you can't afford either, discard the microwave. Jc3s5h (talk) 14:15, 15 October 2011 (UTC)

Getting the wiring brought up to modern standards sounds like a better idea than throwing away a new microwave. Even selling the microwave sounds like a better idea than discarding it. My new GE microwave is nominally 1.7 kw. With noload voltage of 120.5 volts, the microwave in operation drew (measured by Kill-a-watt meter) 14.61 amps, 1612 watts, 1720VA, at .94 powerfactor, from 117.6 volts under load. I have a 20 amp outlet on a 12 gauge circuit with a 20 amp breaker, and no other load on the circuit. Edison (talk) 20:48, 15 October 2011 (UTC)

By "15-amp outlet", I mean a NEMA 5-15 outlet. --Carnildo (talk) 00:22, 16 October 2011 (UTC)

I don't react positively to an outlet rated at 15 amps supplying 16.5 amps. The code derating in the US typically calls for keeping things 20% below the rating, so that a 15 amp outlet would only have to supply a continuous 12 amps. Was the voltage substantially lower than 120? Maybe the device acts like some motors and draws higher current at lower voltage. It is clearly not a resistive load. The Kill-A-Watt also measures voltage, an important aspect of electrical calculations. Edison (talk)

New numbers, based on the discovery that the power consumption fluctuates for the first ten seconds or so: voltage drops from 122 volts open-circuit to 115 volts, the microwave draws 16 amps, 1750 watts, 1850VA, with a power factor of 0.94. Cooking power from measuring the change in the temperature of 1L of water is around 1200 watts. The official ratings are 1600 watts power draw, 1100 watts cooking power. Do these numbers mean "return an obviously defective product", or do they mean "have an electrician install a 20-amp outlet to plug it in to"? --Carnildo (talk) 23:33, 16 October 2011 (UTC)

Fetuses Upside Down

If a newborn spent a whole week upside down, it seems obvious that there would be negative ramifications, but such was the case a week prior to birth. Why (I'm seeking physiologically-based answers) is this (colloquially speaking) blood-to-the-brain issue not a problem for umbilically fed and oxygenated womb dwellers? Peter Michner (talk) 13:06, 15 October 2011 (UTC)

1. Fetuses have a heart rate of 140-160, much higher than average (=> blood is circulating well).

2. they have time to adapt, this movement to turn upside down last several days.

3. Note that the baby doesn't spend a week upside-down. It is upside-down in relation to the mother, who will by laying at her back or side sometimes. Quest09 (talk) 13:25, 15 October 2011 (UTC)

Note that while pressure will be higher at the lower end of the fetus, the pressure of the surrounding amniotic fluid should also be higher at the lower end of the uterus, so it shouldn't be quite the same veins-bulging-out-on-the-side-of-the-head effect. Wnt (talk) 14:04, 15 October 2011 (UTC)

Wnt's got the right answer. There's no ill effect from being upside down if you're under water. Dauto (talk) 14:10, 15 October 2011 (UTC)

I doubt the difference in pressure matters at all here or that there is not ill effect underwater. Quest09 (talk) 14:23, 15 October 2011 (UTC)

You doubt the difference in pressure matters? What else do you think is different between being right-side-up and up-side-down, if not the pressure? Dauto (talk) 22:39, 15 October 2011 (UTC)

The problem is certainly not the external pressure on your body. The problem is how your blood is flowing when your head is on the 'wrong' place. Quest09 (talk) 22:47, 15 October 2011 (UTC)

How does your body know the head is in the wrong place if not because of the external pressure? You haven't proposed any alternate mechanism. External pressure would prevent blood flushing up to someone's head which the cause of discomfort. Dauto (talk) 01:20, 16 October 2011 (UTC)

Knowing the position of your head (and other body parts) relative to the rest of the body is a complex set of physiological/neurologic processes known as "proprioceptive senses" See Proprioception. --Jayron32 01:48, 16 October 2011 (UTC)

Thanks for that, but that's really not the point here. Dauto (talk) 10:09, 16 October 2011 (UTC)

Jayron's comment is on topic: your body cannot feel the difference between external pressure on your feet and external pressure on your head. The difference is simply too small, when both parts are in the same medium. Being at a different position feels different because your blood flows in a quite different way when your heart is below your head, at the same plane as it or above your heart. It's a physiological problem. Quest09 (talk) 12:40, 16 October 2011 (UTC)

The pressure difference between the head and the foot of a grown up man underwater is about 2.5 PSIs. Believe me, you can feel that. If you take a quick look at the article hydrostatic equilibrium you will see that the reason the relative position of the heart and the head matter is because the different relative positions lead to different PRESSURES at the head. Dauto (talk) 13:26, 16 October 2011 (UTC)

You are right about the 2.5 Psi difference. However, it's not much relevant to the flowing of blood within your organism. Human organisms contain a high proportion of liquids that practically do not shrink. The same applies to bones. What you feel by diving is the external pressure on your inner cavities, soft spots and the like. Nothing that would alter your circulation. And that difference in pressure within a uterus is caused by some cm of difference. If you apply the formula .445 psi/foot (1 kg/cm2 per 9.75 meters when in sewater), you'll see how little the external pressure difference is. Nothing comparable to the internal pressure of your blood in your head, when you lay on your side or are upside-down. Quest09 (talk) 14:05, 16 October 2011 (UTC)

Yes, it is comparable to the internal pressure of the body in the head because that pressure is caused by the blood which has a density very close to the density of water since it is mostly water. The fact that most of our body doesn't shrink is completely irrelevant. The shrinkage (or lack of it) has no effect, the pressure does. Dauto (talk) 14:24, 16 October 2011 (UTC)

I didn't say is not comparable. I said it's not relevant. The external pressure cannot compensate for that extra pressure in your head, caused, by the blood, when you are upside-down. That our head does not shrink with pressure is very relevant here.Quest09 (talk) 14:38, 16 October 2011 (UTC)

Yes, it can compensate. The internal and external pressures will produce equal forces in opposite directions that cancel each other. Pressure as such doesn't do any thing. It's the gradient of pressure that can do harm and the external pressure will be equal to the internal pressure - zero gradient - no harm. Even if you are upside down. Dauto (talk) 16:33, 16 October 2011 (UTC)

External pressure won't be much of an issue here, since pre-natal babies are not only with their heads underwater, but all their respiratory track, inner ears, etc, is underwater too, which compensates for any discomfort. 88.11.244.183 (talk) 15:30, 16 October 2011 (UTC)

That's what I've been trying to explain above. The external and the internal pressure compensate for each other leading to no discomfort. Dauto (talk) 16:33, 16 October 2011 (UTC)

The question was not about discomfort, which is irrelevant. But about negative ramifications, and the OP was asking for physiological mechanisms to compensate for that. The pressure on your inner ear might be uncomfortable but your blood sluggishly flowing within your brain is a real medical issue, that won't be compensated by any external pressure. It is compensated by the higher heart rate (2x). Quest09 (talk) 16:56, 16 October 2011 (UTC)

You have amply demonstrated that you do not know what you're talking about. The heart rate has nothing to do with being upside down. The heart rate is the same before the fetus flips upside down. The heart rate is what it is because of the small heart size given the oxygen requirements. Dauto (talk) 17:24, 16 October 2011 (UTC)

Dauto, I think you are unable to understand English properly. In the same way you didn't understand what I was saying before, you did not understand that I never said the heart rate changed due to baby being upside-down. The fetus can put up being upside down due to the high circulation of its blood. The external pressure cannot affect the internal pressure of blood in the brain. My only explanation to your inability to understand is that you are a troll and/or have a deficient level at natural science. Quest09 (talk) 19:32, 16 October 2011 (UTC)

Heh, you would have been hard pressed to find a less deserving target for those charges, even if you'd hunted around here for weeks. Wnt (talk) 21:23, 16 October 2011 (UTC)

Ok, ok, you both: let me try to set things straight. External pressure on your head matters for some things, like your inner ear. It can be compensated by the internal pressure, but that's not the most important problem here. Regarding blood pressure: the heart, in a human being, is centered pretty close to the head, so it does not have to pump blood very high. When you are upside-down, the heart will have to pump blood to a much higher altitude to reach your feet. Additional problems are stroke, and the pressure on your eyes (maybe this external pressure can compensate here, but I'm not sure). Another problem: normally gravity makes the blood flow out of your skull. Upside-down that doesn't work very well. So, fetuses need that 150+ heart rate, for many things, but also for pumping well the blood. Anyone wants to confirm or deny that? 88.14.199.36 (talk) 20:30, 16 October 2011 (UTC)

The pressure difference, which is abolished by amniotic fluid, matters for many things - the eardrum, veins on the side of the head or the white of the eye, accumulation of fluid (edema) See G-suit, which works a lot like amniotic fluid for the adult in a 9-gee turn). Putting pressure on the outside compensates for this difference, however. In air the pressure in the brain of the upside down fetus is a bit larger than in the heart (though because they're so small, this difference is very small, being roughly equal to the weight per square area of the vertical column of water separating them). This is also true in amniotic fluid, but there the external pressure is greater also. As a result, the flesh is under no net pressure to expand and blood can't pool up and expand the head or anything in it. (I suppose this might not be entirely true if the skull were fully ossified, in which case something - either CSF or blood - would move to reflect the change in pressure without a change in volume. The heart may be pumping down into an area of greater pressure, but the weight of the water opposes that pressure. Intuitively, if you take a goldfish bowl and stir it, you don't expect to see vertical circulation hindered because of the differences in pressure at the top and bottom - because the sides press in to compensate and prevent pooling.

Now there are a few things for which the absolute pressure matters - for example, if you had an altimeter in the fetus' head, it could sense whether it was upside down. A little more nitrogen could stay dissolved in the blood in the head versus the heart. But these are all, so far as I can think of, really really minor effects.

I don't see the connection between high circulation of the blood and being upside down. I suspect there must be some scaling law involved in circulation, because one thinks of anything - shrews^{1200 bpm}, birds, mice, whatever - that is very small as having a heart that beats really fast compared to their larger cousins. Wnt (talk) 21:18, 16 October 2011 (UTC)

Recently born babies do not have a high heart beat, It decreases abruptly in the first minute after birth. So, although you are right about small animals having a high heart beat, that does not apply to humans, unless they are in the uterus. Added to that is the fact that the heart beat increases in the weeks before the delivery (some time before the fetus turns upside-down). The heart beat and necessarily higher circulation has probably other advantages. It also delivers oxygen, when oxygen is needed.

The problem with the pressure in the head is not that it could expand it. Quite in contrary. The veins and arteries in our legs, but not in our brains, are made to withstand a higher pressure. I don't know how fetuses cope with that, but it's sure there is something there that hinders them to burst (not the amniotic fluid, which is around the skull, and not around the vessels which are getting a higher blood pressure).

I don't believe the G-suit works like amniotic fluid. It only works because it avoid blood from pooling in the legs during acceleration. 88.8.75.87 (talk) 22:53, 16 October 2011 (UTC)

The G-suit is actually a very good analogy. The amniotic fluid will in fact keep the blood from pooling in the fetus head. You have to keep in mind that the skull of a fetus is still very soft, otherwise birth would be impossible, and will allow the higher amniotic fluid pressure to be translated into higher intro-cranium pressure. @Quest09: My English is fine, I'm not a troll, and I have a PhD in physics, --Dauto (talk) 00:36, 17 October 2011 (UTC)

I'm not seeing much support for any large drop in heartrate after birth (e.g. PMID 20444810). Given how much else is going on, I'd be hesitant to attribute any small change to this. Wnt (talk) 03:30, 17 October 2011 (UTC)

9/11 analysis

Do any articles discuss the fact that the date of ground breaking for the Pentagon was exactly 60 years (by date) prior to the attack upon and collapse of the WTC? --DeeperQA (talk) 16:28, 15 October 2011 (UTC)

The only 9/11-related numerology that seems meaningful to me is the fact that Al Qaeda's second-largest attack, the 2004 Madrid train bombings, took place on March 11, exactly the opposite day of the year from September 11. That seems unlikely to be a coincidence. Looie496 (talk) 17:23, 15 October 2011 (UTC)

The date is right, but why would any coincidence matter at all? Coincidences are everywhere...Quest09 (talk) 20:25, 15 October 2011 (UTC)

Sometimes little cricket, coincidence connected. --DeeperQA (talk) 22:34, 15 October 2011 (UTC)

Some coincidences do matter. For example, the Oklahoma City bombing took place on April 19, the same date as the catastrophic ending of the Waco siege, and that was entirely intentional. Looie496 (talk) 22:49, 15 October 2011 (UTC)

But would you call that something more than trivia? Just remember that in both terror attacks the masterminds where out of their minds. Quest09 (talk) 23:41, 15 October 2011 (UTC)

Nov 11th is Veteran's Day. --DeeperQA (talk) 23:49, 15 October 2011 (UTC)

Remembrance Day in the Empire, and the day of the the dismissal of the Whitlam government in Australia, and the day of Ned Kelly's hanging. HiLo48 (talk) 00:02, 16 October 2011 (UTC)

And Mar 11th was the Japanese Tsunami! We're on to something here. APL (talk) 00:04, 16 October 2011 (UTC)

It's pretty obvious that the hijackers chose 9/11 because of the 911 (emergency call) connection. The entire act was designed to be symbolic, from the choice of planes to the choice of targets. it's unlikely that they would have delayed the act until the correct year for a symbolic gesture that almost no one in the nation would have recognized (I mean, how many Americans know the ground-breaking date for the pentagon?) that would have greatly increased the risk of discovery for almost no symbolic benefit. it's just a coincidence. --Ludwigs2 00:25, 16 October 2011 (UTC)

on the "pretty obvious" comment. I think its pretty obvious that the connection you note is a random coincidence; and since you have made the positive assertion that there is a connection between the two numbers, you should have to, you know, back it up with good evidence... --Jayron32 00:35, 16 October 2011 (UTC)

Yeah, I was about to raise the same point. I've never heard it suggested before that it was deliberate in that way. So, source? HiLo48 (talk) 00:45, 16 October 2011 (UTC)

The 9/11 Commission Report says (on page 249) that the exact date of the attack was not chosen until mid-August 2001, and was chosen by Atta (not KSM or OBL). OBL wanted it done as soon as possible, but wanted the date chosen at the last minute, so that it would be hard to break up, or something like that. So it's not clear there was huge symbolism put on the actual choice of date. Maybe Atta thought it was a nice coincidence or something like that, but it doesn't seem like this was a top-level choice by either of the main planners, but by the guy who bought the plane tickets. I find it terribly unlikely that Atta timed it to coincide with the groundbreaking of the Pentagon. --Mr.98 (talk) 02:18, 16 October 2011 (UTC)

What I saw about the particular date chosen that made it all the more successful for the terrorists was that it was a beautiful day. The clear skies and sunshine made the global TV coverage about as dramatic as it could be. A cloudy or stormy day would have lessened the impact considerably. But again, just (bad) luck, I imagine. HiLo48 (talk) 02:25, 16 October 2011 (UTC)

But given that the date was chosen three weeks in advance, it seems hard to believe they were really all that aware of how nice or not nice it would be. I also seem to recall it raining that evening or the next day, which complicated rescue/recovery efforts. --Mr.98 (talk) 12:06, 16 October 2011 (UTC)

(un-indent): Foreigns rarely see the 9/11 as september, 11. That day was for most just 11/9. And many don't know that 911 is the emergency number, specially those who have never been to the US and do not watch much American fiction. 88.11.244.183 (talk) 15:35, 16 October 2011 (UTC)

It's also the case that Atta, when transmitting the date to the al Qaeda bigwigs, did so as 11/9 (he has some sort of dopey code about two dashes a slash and a lollipop... which would be funny if it wasn't so grim). That being said, I would be somewhat surprised if he didn't know 911 was an emergency code in the USA — surely our export of entertainment worldwide has conveyed that to a few people? But there isn't really any evidence that he chose it for any particularly symbolic reason. --Mr.98 (talk) 02:08, 17 October 2011 (UTC)

For enough coincidences, just see September_11. 88.11.244.183 (talk) 15:43, 16 October 2011 (UTC)

nucleotide reformation

If you diced up a bunch of DNA and RNA in water so that no more of the helix remained intact and allowed it to stand in say a beaker through varying condition of heat and cold, electrostatic and magnetic influence, light and dark and organic and inorganic chemical exposures and reactions would any helices or composite pieces spontaneously or otherwise form? --DeeperQA (talk) 16:47, 15 October 2011 (UTC)

Yes. It's called self assembly. You might like reading DNA nanotechnology. Dauto (talk) 22:45, 15 October 2011 (UTC)

Actually, you won't get any self assembly of DNA or RNA threads without throwing a lot more into the mix. When DNA and RNA are cut into nucleotides, you end up with mononucleotides, consisting of a base, covalently bound to a five-carbon sugar, covalently linked to one phosphate group. To get nucleotides to assemble into threads, you need a source of energy for creating the covalent bonds from the phosphate group of one nucleotide to the sugar group of the next nucleotide. When synthesising DNA and RNA, cells use trinucleotides, which have three instead of one phosphate group. The energy comes from splitting off the two extra phosphate groups from the trinucleotides (cells use a lot of other stuff too, like enzymes and a pre-existing DNA-thread). In your question, you allowed for "organic and inorganic chemical exposures". If you want to use your mixture of mononucleotides for synthesis of DNA threads, you might try some modification of one of the techniques described in the oligonucleotide synthesis article. And since you mention heat and cold, take a look at the Polymerase chain reaction article (requires pre-existing DNA, trinucleotides instead of mononucleotides, and a bacterial enzyme, though). --NorwegianBlue ^talk 20:41, 16 October 2011 (UTC)

Speed of a falling person

So, I'm writing a novel and in it, someone was falling from a floor near the middle of the cruise ship, and they were falling from about 90-100 ft high (from the deck to the water, not from the deck to the keel), and I wanted to determine the approximate speed he would have fallen to land in the water. Is it possible to determine this? If it is, what do you guys think it would be? Thanks! 64.229.153.152 (talk) 17:44, 15 October 2011 (UTC)

Yes, given all of the necessary parameters. --DeeperQA (talk) 17:57, 15 October 2011 (UTC)

For that distance, you can reasonably leave out things like drag and go with v=sqrt(2gd) (from equations for a falling body). Speed at impact would be, give or take, 25 m/s or 55 mph. — Lomn 18:04, 15 October 2011 (UTC)

As Lomn says, there won't be much difference. Anyways, I explain anyways. It depends on what he is wearing. The more resistance to air it offers, the less he will accelerate. A person with simple summer clothes will hit the water faster than, say, a person with winter clothes and half-opened coat that will behave like a sail in the wind. You can play with this without actually giving any hard figure.

By the way, falling speed does not depend of weight/mass Galileo's Leaning Tower of Pisa experiment (actually, it does depend of the relative mass of the attracting bodies, in this case Earth and the person, but Earth is so ridiculously huge in comparison to the person, that two persons of different mass will suffer approximately the same attracting force towards Earth). So, a fat person will fall a bit slower than a thin person because he offers more resistance to air. --Enric Naval (talk) 18:11, 15 October 2011 (UTC)

No. Falling speed does not depend on weight only when you do not take wind resistance into account. When you do, you are balancing the force of gravity (weight) versus the wind resistance (drag). A block of styrofoam will fall more slowly than one embedded with a bowling ball, and given the square / cube relation of surface area to weight, the fat man will fall more slowly than the thin one. Just ask a skinny skydiver who has to arch like hell to keep up with his heavier formation companions. -- 110.49.27.51 (talk) 00:35, 16 October 2011 (UTC)

The bowling ball needs to be exactly in the center of mass of the block, or the blocks will have different behaviour when falling, causing different air drag. Try using spheres of styrofoam with a well-centered bowling ball, and they will fall at the same speed. If you use irregular bodies that have different drag depending on its position, you are adding extra variables into the equation that muddle the results. Both objects needs to be the same shape and have the center of mass in the same place, or they will have different air drag and fall at different speeds, even if they weight the same.

No, the fat man falls slower only because he has more air drag. Having the center of mass in the belly might cause some differences in their posture, changing the air drag. Our Natural Sciences teacher made once a demonstration: let fall a sheet of paper, and it falls very slowly, now crush the paper, let it fall again, and it will fall very quickly. It has exactly the same mass, the only difference is that the crushed paper has less air drag.

Again, the force made by gravity is always the same, our mass is too small to have an effect, see for example Gravity#Earth.27s_gravity. --Enric Naval (talk) 10:15, 17 October 2011 (UTC)

P.D.: for that distance it doesn't have time to reach Terminal velocity (about +50 m/s[2]), so the person will accelerate during all the fall. --Enric Naval (talk) 18:15, 15 October 2011 (UTC)

Oh, okay, well, it'd be shorts with a t-shirt and he would probably be about 135 pounds? It's a teenager, so. 64.229.153.152 (talk) 18:17, 15 October 2011 (UTC)

Note that there are also environmental factors independent of the person such as updrafts and downdrafts or even air pressure. However, all said, I'll stick with my initial post: a person will be traveling 25 m/s in the vertical after falling for 30 meters, barring exceptional circumstances. None of what Enric or I have mentioned (weather, standard clothing, mass of person) are sufficiently exceptional to meaningfully impact this answer. — Lomn 18:26, 15 October 2011 (UTC)

Unmentioned parameters like holding onto a bunch of party balloons filled with helium or wearing a skydiver parachute or repelling off the side of the boat, even holding a surfboard would most likely decrease the rate of descent unless there was a strong downdraft that might actually increase it, not to mention whether or not the surface of the water was descending or elevating.. --DeeperQA (talk) 18:34, 15 October 2011 (UTC)

@OP, Lomn has mentioned the formula "v=sqrt(2gd)", which translates to "velocity = square root of (2 multiplied for acceleration 9.8 multiplied per distance in meters)", or $\ v={\sqrt {2*9.8*distance}}\$. You will have to translate feets to meters.

(Note: the formula doesn't take the person's mass into account. That's because, as said above, a person's mass is so small when compared to Earth's mass that we simply use the standard acceleration value of 9.8 m/s², known as "g".) --Enric Naval (talk) 18:53, 15 October 2011 (UTC)

But according to the OP she (or he) is writing a novel and novel's are fiction although they may be based upon fact or incorporate fact. A novel that includes facts about a Tsunami might have the person falling all the way to the bottom of the Tsunami's displacement which would increase distance perhaps significantly resulting in a faster speed. It is important to know the exact distance of the drop to be accurate as to speed. --DeeperQA (talk) 19:18, 15 October 2011 (UTC)

Okay, I determined the height of the deck he would have fallen out of would be 115 ft from the sea, standing vertically erect with his arms to the side wearing no heavy clothing that could cause resistance. 64.229.153.152 (talk) 20:37, 15 October 2011 (UTC)

A little farther, a little faster. Call it "about 60 mph" and you'll be correct enough that pedants won't have a legitimate argument against you. In any event, is there any pressing need for an estimate more accurate than +/- 10 mph? It's far enough to fall fatally (in which case nobody will need to know that he hit at exactly 59.57 mph when his neck snapped); it's far enough to fall survivably (in which case he'll brag about hitting the water at over 60 mph with nary a bruise to show, and no one will believe him or care anyway). — Lomn 22:53, 15 October 2011 (UTC)

115 feet is "only" 35 meters. Applying the above formula, he could only reach 26.2 m/s, discounting wind drag, etc.

See Free_fall#Surviving_falls. 50% of children survive a fall from a 4 storey building, which is a bit over 35 feet, I think (a building storey is about 9 feet tall?). There are several people who have survived falls from thousands of meters. I have seen people jumping from the "Salto de Bierge", a 35 feet tall artificial waterfall, people are instructed to jump in vertical position with their arms across their chest. I assume that this is a good shock-absorbing position for hitting water. (Of course, hitting the water head first can hurt very badly your neck, not to mention that the basin below is quite shallow and you could hit the rock bottom).

The highest Diving platform is 33 feet. --Enric Naval (talk) 10:15, 17 October 2011 (UTC)

La Quebrada Cliff Divers jump from 148 feet, see HowStuffWorks for more info on the injuries that you can sustain if you don't fall feet first[3]. --Enric Naval (talk) 10:20, 17 October 2011 (UTC)

Free electronic (CFL) ballast schematic?

It would be really neat to have the above picture and a schematic with explanation how it works at an electrical level. Is there any schematic for a CFL ballast that is free enough to be included on wikipedia?

These vary from bulb to bulb because the optimum characteristics depend on things like the unwrapped length of the bulb tube, its width, the latest formulation of the tube gas and coatings, and they're already many revisions in for fire safety. Dualus (talk) 04:50, 16 October 2011 (UTC)

I know, but the point is to use one schematic as an example.Electron9 (talk) 08:59, 16 October 2011 (UTC)

Maybe a block diagram would be better, because small changes in the design requirements under so many conditions on AC circuits could have profound changes in the best circuit. The goal is to start the light quickly and degrade safely in overheating conditions, which interacts with component placement and type selection, so it's not clear that any schematic or block diagram would even be able to capture both of those goals. Dualus (talk) 18:07, 16 October 2011 (UTC)

An example won't cover everything. It has never been the intention. Actual applications will vary. But with a starting point it's much easier to understand. Electron9 (talk) 18:30, 16 October 2011 (UTC)

Okay, but if you try this you are liable to introduce transient noise in your power system which could interfere with delicate components, so it should be on a surge protector, and if anything in your house is using the power circuit for data, the bandwidth will go down. Also, I have read it could be a fire risk, or at least it was in one manufacturer's recalled revision. Dualus (talk) 23:16, 16 October 2011 (UTC)

The schematic is All materials on this site copyright ©2011 UBM Electronics, besides CFL dimming makes it unnecessary complex and is an flawed afterthought. I was looking for a free schematic. Electron9 (talk) 03:27, 17 October 2011 (UTC)

Although these schematics will not be free, common parts are visible. [4]. -Yyy (talk) 07:38, 17 October 2011 (UTC)

I know that site since long, but the schematic pictures are copyrighted by pavo. And the connection setup by itself ie the netlist is likely copyrighted by their respective manufacturers. So any truly free schematic out there? ;) Electron9 (talk) 16:57, 18 October 2011 (UTC)

I did not meant to use these images as is, I meant to draw schematics yourself, using common components in all images. Here is a (not very good quality) sample (that big box in middle is an inverter, which contains 2 transistors, 3winding transformer(that round, brown thing in photo) and other components). All lamps in that site (and all lamps, which i have disassembled) had at least these components in this order. Some lamps has an additional inductor between input capacitor and inverter. Probably it would be possible to draw a generalized schematics of inverter, too. Also, there is a document describing various types of fluorescent lamp ballasts [5], according to that document most (all encountered) CFLs uses a voltage fed quasi-resonant circuit (paragraph 3.1 in linked document). -Yyy (talk) 10:00, 19 October 2011 (UTC)

Also commons category commons:Category:Wiring diagrams of fluorescent lamp power supplies contains several schematics. -Yyy (talk) 10:09, 19 October 2011 (UTC)

Thanks!, does it work in IRL? or miss essential features.. Electron9 (talk) 01:30, 20 October 2011 (UTC)

marine electrical engineering

In a ship, where do we get the ground/earth is connected to?In a 3 phase supply, where does the neutral is connected to in a ship normally? — Preceding unsigned comment added by 223.176.157.104 (talk) 19:12, 15 October 2011 (UTC)

Nothing said here should be taken as instruction or advice as to safe or legal practices. Consult a qualified engineer for such advice. Wiring practices on ships varied over time and between countries. In the earliest years of electricity on ships, some countries used the metal ship hull and structure as a ground and neutral, while some other countries didn't. Thus varying practices may be found depending on how old a ship is and what country it is from. Here is the US Code of Federal Regulations, 2009 edition, with rules for electrical wiring on shipping under jurisdiction of the US Coast Guard, which says section 111.05-11 "A vessel's hull must not carry current as a conductor except for the following systems (exceptions are listed). Then they refer to "grounding of the neutral" at one point, at the generator switchboard. They do not describe the "ground" but it might well be the metal hull of the vessel. On a wooden or fiberglas boat, it is unclear what the "ground" would be. Grounding (section 111.05-1 is to "prevent a voltage above ground on the enclosure materials) such as conduits and panel enclosures.Enclosures are connected to a grounding conductor. During normal operation, the ground carries little or no current. Edison (talk) 20:32, 15 October 2011 (UTC)

I may be completely missing something fundamental, but could they not use the water as a ground the same way lightning rods are grounded into the earth? (I'm assuming "ground" in this situation isn't something completely different, but I may be wrong given I have a very limited knowledge of this stuff). Ks0stm ^{(T•C•G•E)} 02:07, 16 October 2011 (UTC)

Does Lightning_rod#Watercraft_protectors help at all? Pfly (talk) 04:36, 16 October 2011 (UTC)

If a ship has a metal hull, would the paint on it isolate it from the surrounding water? How about a fiberglass or wood hull? I suppose a ground connection to the copper bottom on a wood ship could "ground" it to the surrounding water. I suppose a ship could have ground wires or bare metal ground plates in contact with the surrounding water, but I found no mention of this. Please realize that single phase or three phase generators, with their phase and neutral conductors, can power lights and motors without a connection to the Earth, just as in airplanes or spacecraft. Edison (talk) 04:39, 16 October 2011 (UTC)

Ok, well that somewhat explains it. I'm pretty sure it's pretty far off from what the original poster was asking given your answer, but I figured it made enough sense to me that I might as well bring it up. Thanks for the explanation.` Ks0stm ^{(T•C•G•E)} 05:18, 16 October 2011 (UTC)

well thank you everyone for the contribution but a ship is not grounded in a conventional way.If they connect the ground to the hull there is a possibility of electric shock is someone touches the hull & we know salt water(sea water) is a great conductor of electricity but ship is not grounded to the sea water by using metal projection like the way it is done for normal grounding. "Insulated neutral system" is preferred in a ship but in that case where is the neutral connected?? anybody..? — Preceding unsigned comment added by 110.227.141.56 (talk) 13:46, 16 October 2011 (UTC)

According to 'Electrical Grounding on Ships', the neutral is not connected to anything. The article explains why. --Heron (talk) 19:10, 16 October 2011 (UTC)

So far there are two claims, seemingly in conflict. I cited the US Code, which calls for grounding the neutral at the switchboard, and Heron says "the neutral is not connected to anything." Could Heron's source really be saying that the "isolated neutral" is only grounded at one point, at the generator panel? Industrial power systems sometimes have isolated three phase three wire power, with no intentional ground on the circuit supplying three phase motors, but with ground detector lights or relays to let the operator know when there is a ground fault. On such a system, the first ground fault does not cause a surge of current. The equipment can then be shut down to find and fix the ground fault in an orderly manner. How and when such a system can be used is strictly regulated by applicable electrical codes. Any phase conductor can become elevated to a high voltage above ground when another phase gets grounded, or when there is a short to a primary conductor. 19:29, 16 October 2011 (UTC)

As I read the US Code, it says (§111.05-17) that if the generator has a neutral then it must be grounded at the switchboard, as you say. However, the code (§111.05-25) also allows for ungrounded systems, which is what my source describes. What we haven't established yet is the relative popularity of the two systems. 'Come Back to Ground!' is a good overview of different systems around the world, but unfortunately it's not signed or dated. --Heron (talk) 09:49, 17 October 2011 (UTC)